This invention relates to the treatment of silica, particularly silica-supported chromium catalysts suitable for olefin polymerization.
Supported chromium oxide catalysts can be used to prepare olefin polymers in a hydrocarbon solution to give a product having characteristics from many standpoints. Supported chromium oxide catalysts can also be used to prepare olefin polymers in a slurry system wherein the polymer is produced in the form of small particles of solid material suspended in a diluent. This process, frequently referred to as a particle-form process, has the advantage of being less complex. However, certain control operations which are easily carried out in the solution process are considerably more difficult in the particle-form process. For instance, in the solution process, control of the molecular weight can be effected by changing the temperature with lower molecular weight (higher melt flow) being obtained at the higher temperatures. However, in the slurry process, this technique is inherently limited since any effort to increase the melt flow to any appreciable extent by increasing temperature will cause the polymer to go into solution and thus destroy this slurry or particle-form process. Also it is, of course, desirable to achieve high catalyst activity so as to make more efficient use of a given size reactor.